Using DHCP as optional feature SG350

[ChristianGaber]

Hello,

we have SG350 Switches.

We want to use two of them e.g. today with activated dhcp server for two separated small networks. Tomorrow we want to connect two switches because we need a bigger network, but of course then I have to deactivate one DHCP server.

Now we don't want to change everytime the configuration. Our Idea is, we're configuring one Port (Port 10) as VLAN 1 with enabled DHCP. All other Ports are in VLAN 2. If we now want to use the switch with activated DHCP then we just put a cable between e.g. Port 9 and 10. I thought this would connect my two virtual networks and the dhcp is now available on VLAN2. But this is not working.

Could you give me please advice what my error is and how to solve my problem? I don't need for anything else two VLANs, so if there is a better solution I would be thankful.

Best regards

Chris

[balaji.bandi]

Make sure you have VLAN 1 SVI and VLAN 2 SVI IP interface created on the switch and add DHCP helper to service DHCP requested for VLAN2

check below document :

https://www.cisco.com/c/en/us/support/docs/smb/switches/cisco-small-business-300-series-managed-switches/smb5567-configure-dynamic-host-configuration-protocol-dhcp-relay-set.html

[ChristianGaber]

Thanks for your Reply,

I'm not completely sure how to make sure having VLAN 1 SVI and VLAN 2 SVI IP. Could you give me a hint for that please?

I have now the DHCP helper activated for vlan2, but current behavior is that as soon as I put a cable between VLAN 1 and VLAN 2 now both Ports are VLAN1.

Thank you

[balaji.bandi]

here is the VLAN SVI configuration :

https://www.cisco.com/c/en/us/support/docs/smb/switches/cisco-350-series-managed-switches/smb5719-configure-vlan-interface-ipv4-address-on-an-sx350-or-sg350x.html

You need to put the respected port to VLAN 2, if not by default all ports belong to VLAN1

[paul driver]

Hello
Its rather confusing what you are have currently switch regards dhcp?

Two L3 switches both running as a dhcp server  service for a single vlan  each OR a single L3 switch that is running the dhcp server service for both vlans.

In either case it would  be just a matter of dropping the dhcp lase timings for either or both dhcp scopes and creating the same scope on the new device and then disabling the old server/scope and enabling the new server/scope.

If you are going to have two switches running DHCP then you could for resiliency even split the dhcp scopes so half of the allocation for both vlans are running on either switch at the same time

So please can you please elaborate further on what is your current topology is regards DHCP and you intentions

[ChristianGaber]

Hello Paul, thanks for your response.

I have one SG350 L3 switch, in a temporary installation, probably every day in a complete different setup (I'm working in the stage audio rental area, one day the switches work for control Network, the next day to build an audio streaming network and the next day it's for sharing the internet connection in the location for multiple computers).

One Day I want to have DHCP activated.

Another Day I want to have DHCP deactivated WITHOUT entering the config page. (so everyone can easily set up the switch as they need it at that day).

I know, once after dhcp is setup, it's just 3 clicks or so to activate/deactivate the DHCP server in the config page, but there are so many things the installers of the temporary setup (not me) can accidently change, thats why I dont want that they have to enter the admin panel in the first way.

My idea to solve that problem was: configuring a DHCP Server which is just active on a single Ethernet Connector (in my case GE10).

If i don't want DHCP I just connect all my devices to GE 1-9 and they can communicate with each other without DHCP server. If the next day I want DHCP I just put a patchcable between GE 9 and GE 10 to put the DHCP server to the other ports. In this case the Users who setup the systems just have to patch a cable or unpatch it to activate or deactivate the dhcp server.

I hope this is more understandable :-)

Best regards